Avoiding Overheating in Existing School Buildings Through Optimized Passive Measures

This study assessed passive strategies to improve summer thermal comfort in school buildings in Karlsruhe, Germany, through building performance simulations. Traditionally, retrofits in this climate focus on reducing heating demand, but rising temperatures now increase overheating risks. Simulations showed that in current conditions, overheating affects up to 27% of occupied hours, particularly in lightweight buildings. Heavyweight buildings can largely avoid overheating through good natural ventilation and ceiling fans. Lightweight buildings require additional sun protection measures—like external shading—along with ventilation improvements to significantly reduce discomfort. With optimized passive strategies, discomfort time could be reduced to less than 5% across all building types. The study also used multi-objective optimization to balance thermal comfort improvements and investment costs. It emphasized that ventilation enhancements, vertical window openings to induce stack effects, and increased air velocity through fans are critical for adapting school buildings to a warming climate. The findings provide targeted guidance for decision-makers to prioritize cost-effective, future-proof retrofits based on building typology.